Heat-sensitive record material



United States Patent US. Cl. 117-363 1 Claim ABSTRACT OF THE DISCLGSUREThere is provided by this invention an improved heatsensitive recordmaterial wherein such material, comprises: (1) a base sheet such aspaper; (2) a coating of finely dispersed acidic particles such as adi-phenol, finely dispersed colorless chromogenic particles such as abenzoindolinospiropyran derivative which give color when in liquidcontact with an acidic material, and a film-forming polymeric materialsuch as polyvinyl alcohol to act as a matrix for the two color-formingreactants; and 0ptionally; (3) a protective overcoat such as a film ofpolyvinyl alcohol which may also have soditun carboxy methyl cellulosepresent in it to give a proper viscosity to the coating slurry for easein machine application; is made resistant to pick-off of the recordsheet surface and freezesticking of the record sheet to the printinghead when the record material is used in conjunction with a rapidlyheated and cooled printing head, particularly one of the planographicclass. The improvement consists of providing the heat-sensitive recordmaterial with a lubricating overcoat comprising a film of hydrophilic,polymeric material, such as polyvinyl alcohol (with or without addedsodium carboxy methyl cellulose), having dispersed therein to the extentof about 2% fine particles of a lubricating or nontacky wax, meltingabout 140 C.; optionally a primer coat of the same composition; andfinally as a further option an added dispersion of calcium stearate inthe coating or layer which bears the colorforming coreactants.

This invention relates to heat-sensitive coated record material thatwill not pick-01f onto hot type surfaces.

Heat-sensitive record materials of the type shown in an application forLetters Patent of the United States, Ser. No. 366,524, filed by Henry H.Baum on May 11, 1964, owe their heat-sensitive characteristics to athermoplastic film coating which contains in it heat-responsivechemically reactive color-producing material in dispersed solidparticulate form. The flowing together of these materials underconditions of the coatings being subjected to a printing contact withhot type causes coloration of the film coating at the typed points.

As long as the applied type is hot as it is withdrawn from contact withthe record material and does not pick up the melted material, all isWell, and there is no picko'if problem to spoil the print or dirty thetype face. However, there have been developed planographic surfaceprinting plates or surfaces that have heatable matrices flush with thelano-surface, which matrices are selectively operable by flash heatingto print the selected symbol. These symbols, for example, may be made upof selected elements of a Solomons Seal type of matrix, which elementsare, individually for an instant, rendered very hot (250 degreescentigrade) and suddenly cooled by heat conduction into a heat sink tomake them ready for printing another selected symbol, the recordmaterial being advanced or moved across the printing plate betweensymbol-printing operations to form a contextual data message. Theheating and sudden cooling of the type face may freeze the melted filmto the printer plate, re-

3,445,261 Patented May 20, 1969 sulting in rupture of the film coatingor its supporting substrate of paper or paper-like material and, inaddition, fouling the printing head. A printer head of the planar matrixtype is disclosed in United States Patent No. 3,161,457, which issued onthe application of Hans Schroeder et al. on Dec. 15, 1964.

A preferred embodiment of a pair of heat-sensitive reactants selectedfrom among those appearing in the Baum disclosure, and as used in acoating system for the purpose of providing the anti-pick recordmaterial of this invention, is the pair comprising, as the colorreactants, (a) the chromogenic material ture and having a melting pointof 156 degrees centigrade. This acidic material will be called Bisphenol A, as it is commonly sold under that designation.

These reactants may be dispersed as solid fine particles in a watersolution of a suitable grade If polyvinyl alcohol and water-wettablecalcium stearate, and the dispersion may be applied to and subsequentlydried on a prepared paper sheet to produce a heat-sensitive coatingwhich responds by blue coloration to hot type pressed thereagainst. Thiscoated sheet has the infirmity, however, of sticking to or picking-offonto a planographic type surface having rapidly heating and coolingconfigurations adjacent to constantly cool areas (room temperature)across which the sheet is passed step by step. The damage to the recordis more apparent with finer printing than with larger printing, as wouldbe obvious, so the invention is mainly directed to a pressing problemwith fineprinting species of planar printing heads. The printing headitself, by picking up the coating, is likewise subject to fouling andconsequently is rendered incapable of giving a sharp print.

It has been found that, by confining the heat-sensitive film coatingbetween an under layer of sheet-supported film material of polyvinylalcohol, sodium carboxymethyl cellulose (CMC), and Acra Wax C, and anoverlayer or top coating of the same material, and by providing theso-sandwiched color-producing film coating with calcium sterateparticles, the sticking, or picking-oil", of the material onto theplanar printing element is prevented, and the sharp print property ispreserved.

Acra Wax C is a reaction product of hydrogenated castor oil andethanola-mine, is insoluble in boiling water, and has a melting point ofto 143 degrees centigrade, a flash point of 285 degrees centigrade (opencup), and a specific gravity of 0.97 at 25 degrees centigrade. It may bepurchased as a fine powder under the quoted brand name from GlycoChemicals, Inc., 417 Fifth Avenue, New York, N.Y., United States ofAmerica. Although Acra Wax C has been specified as preferred, anysimilar anti-blocking wax or nontacky wax in powdered form and insolublein water may be used and will be specified in the claims as nontackyWax.

The calcium stearate used is of fine powder particle size and haswater-Wettable characteristics to permit of its dispersion in a watersolution of polyvinyl alcohol. A suitable material is the Disperso gradeof Witco Chemical Company, Inc., 122 East Forty-Second Street, New York,N.Y., United States of America, but the controlling factor in itsselection, from whatever source it is obtained, is that of itsdispersibility in water, so the preferred embodiment will be specifiedas water-dispersible calcium stearate powder.

The polyvinyl alcohol preferred for the substrate coating (or primer) isa medium-viscosity grade of 99% hydrolysis, and this grade also is usedfor the overcoating. while one of 98% hydrolysis is used for the middlelayer, containing the calcium stearate and the dispersed mixture ofcolor reactants. Water solutions of the specified polyvinyl alcohols gelat room temperature (20 to 25 degrees centigrade). Polyvinyl alcohols ofthis type can be purchased as Elvanol brand from E. I. DuPont de Ncmoursand Company, Inc., of Wilmington, Del., United States of America, theirgrade 71-30 being of 99% hydrolysis and their grade 71-24 being of 98%hydrolysis. The medium-viscosity range of these materials lies between23 and 32 centipoises in a 4% water solution at 20 degrees centigrade asdetermined by the Hoeppler falling-ball method.

The primer and the top coating composition contain sodium carboxy methylcellulose, with enough sodium carboxymethyl groups to make itwater-soluble. This kind of material and the process of making it areset out in the pamphlet Hercules Cellulose Gum Properties and Uses,printed and copyrighted in 1960 by Hercules Powder Company, Wilmington,Del., United States of America. It lends a coating viscosity property tothe coating composition as a whole, but, as it is not an essential inthe coloror mark-forming property of the record material, equivalentsacting with the same physical properties may be substituted therefor.

Other waxes, other metal stearates, and heat-meltable gels of otherwater-soluble polymers having characteristics similar to those of thepreferred materials may be substituted because these materials are usedfor their physical characteristics of antitackiness, temperaturemelting, film-forming characteristics, and general aptitude for forminga compatible reaction environment for the color reactants.

EXAMPLE I In this, the preferred, embodiment, the substrate is bondpaper of 13 pounds weight per ream of 500 sheets 17 by 22 inches havinga medium calendered surface.

The primer coating for it when dried is one pound per specified ream,and the wet composition is as follows:

Percent solids Polyvinyl alcohol (99% +hydrolyzed) 73 Sodiumcarboxymethyl cellulose (water-soluble) 25 Acra Wax C 2 Water, to make asuitable coating dispersion.

The color-reactant-containing middle coating of 3.25 pounds perspecified ream is as follows:

Percent solids 6-Cl, 8-OCH BIPS 15 Polyvinyl alcohol (98% hydrolyzed) 15Bis phenol A 65 Calcium stearate water-wettable The BIPS type ofcompound may color slightly prematurely on aging, and this may beprevented by adding to the composition of the coating several percent ofthe compound 2,4-bis-acetoamido ethane. As a practical matter in makinga water solution-dispersion of the solids, a nominal amount of defoamingand dispersing agents may be used.

The top coating is 1.75 pounds per specified ream (dry) of the samecomposition used for the primer coating.

The essential feature of the invention is the use of powdered nontackywax in the primer coating and the top coating, and a small percentage ofa metal stearate in the middle coating, which contains thecolor-reactant com ponents, the latter not being restricted to thepatricular MP8 or to the acid phenolic material noted in the preferredexample but being applicable, for example, where the reactant systemsmay be selected from among the many disclosed in the Baum United Statespatent application to which reference has been made. Another pair ofcolor reactants useful and representing another type of chromogenicmaterial is crystal violet lactone and Bis phenol A.

The practitioner of this invention may use the solid powderednontacky-when-melted wax in any record material coating meant to bemelted to cause the bringing together of the color reactants andotherwise having a composition tending to be picked-off by hot typemembers as they are cooled.

EXAMPLE II This is the same as Example I except that the primer coatingis omitted. The heat-sensitive record material of this example performssatisfactorily, but it is not as completely free of film-coating rupturewhen in contact with the printing head as the material of Example Iwhich has been designated the preferred embodiment.

I claim:

1. In a record material including a base sheet having a coating ofheat-meltable hydrophilic film-forming material having dispersed in thecoating powdered chromogenic material of substantially colorless stateand particles of heat-meltable acid phenol compound which when in liquidcontact with the chromogenic material reacts therewith to form color,the improvement of also including an overcoating of polymericfilm-forming material of hydrophilic characteristics having dispersedtherein to the extent of about 2 percent particles of a wax nonblockingwhen melted, said polymeric film-forming material consisting of aboutthree parts of polyvinyl alcohol and about one part of water-solublesodium carboxy methyl cellulose.

References Cited UNITED STATES PATENTS 2,348,128 5/1944 Groak 11736.42,777,781 1/ 1957 Kordig et al 117-3 6.4 2,943,952 7/ 1960 Clark 1l736.43,062,676 11/ 1962 Newman et al 117-36.4 3,076,721 2/ 1963 Coles et al.1l736.9 3,108,896 10/1963 Owen 117 36.9 3,111,423 11/1963 Ostlie117-36.9 3,244,550 5/1966 Farnham et al. 11736.8 3,347,696 10/1967Newman 11736.4

FOREIGN PATENTS 953,150 3/1964 Great Britain.

MURRAY KATZ, Primary Examiner.

US. Cl. X.R.

